"Like you," he told Issa and Grassley on Wednesday, "the department is deeply interested in understanding the facts surrounding Operation Fast and Furious."

Mexican authorities have long complained that most of the guns that fuel the drug wars there are purchased in the U.S.

On Wednesday, Mexican federal police released a videotaped interrogation with recently captured Jesus Rejon Aguilar, an alleged founder of the Zetas gang who is wanted in the slaying of a U.S. immigration agent in Mexico. He brazenly told them that "all the weapons are bought in the United States" and that "even the American government itself was selling the weapons."